1. Field of the Invention
The present invention relates to a biomaterial that can be used for artificial bone, artificial teeth roots, and artificial joints and the like, a film with apatite forming ability which covers the surface of this biomaterial, and a coating liquid capable of forming this film.
2. Description of the Related Art
Artificial bone, artificial teeth roots and artificial joints and the like are placed inside living bodies, and must consequently display bioaffinity, in order to prevent being rejected as foreign matter.
The crystalline structure of apatites such as hydroxyapatite [Ca10(PO4)6(OH)2] closely resembles the crystalline structure of biosystems such as bone and teeth, and apatites have been confirmed as displaying good bioaffinity, enabling them to be integrated with biosystems inside living bodies.
Taking advantage of this characteristic, hydroxyapatite is conventionally used to coat the surface of metals such as stainless steel and titanium alloy, or ceramics such as zirconia, which are used as the base materials for biomaterials such as artificial bone, artificial teeth roots, and artificial joints, thereby forming a surface layer that imparts bioaffinity to the biomaterial.
Many methods have been proposed for forming this surface layer of hydroxyapatite on the base material.
A first method is disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 62-34559, and involves coating the hydroxyapatite directly onto the base material using plasma spraying.
A second method is disclosed in Japanese Examined Patent Application, Second Publication No. Hei 2-13580, and comprises a sintering method used in the production of a terminal for use with living organisms.
Furthermore, a third method involves injecting calcium ions into the surface of a titanium base material, and then immersing the base material in a simulated body fluid. In addition, a fourth method involves treating a base material of titanium with a high concentration aqueous alkali solution, conducting subsequent heat treatment at 600° C., and then immersing the base material in a simulated body fluid.
However, in the plasma spraying of the first method described above, the high temperature heat treatment causes the raw material hydroxyapatite to melt, which can result in the formation of a different type of hydroxyapatite, and an undesirable lowering of the bioaffinity. Additional problems also arise in that the formation of a dense layer of hydroxyapatite is difficult, the adhesion between the base material and the hydroxyapatite is poor, leading to very low yields, and the fact that the method requires expensive equipment.
In the second method, namely the sintering method, the high temperature heat treatment causes the raw material hydroxyapatite to melt, which can result in the formation of a different type of hydroxyapatite, and an undesirable lowering of the bioaffinity. Furthermore, in the third method described above, the ion injection of calcium ions requires expensive equipment, and moreover, the surface of the coated base material is prone to distortion and the occurrence of defects. The fourth method requires both treatment with a high concentration aqueous alkali solution, and a high temperature heat treatment, and this takes time and effort, leading to increased costs.